Lynch was given just over six weeks to retain the marginal seat of Halifax for Labour having been selected as the party's candidate only at the end of March 2015.[2]

Labour's search for a new candidate was triggered by the decision of sitting MP Linda Riordan in February to stand down on health grounds.[3] Her decision, and Lynch's subsequent selection, set up one of the most closely fought contests in Yorkshire in the election.

Riordan had held Halifax for Labour in 2010 by a majority of just 1,472 votes, and the seat was considered a key target for the Conservative Party.[4] Lynch was successful on election night and held the Halifax seat for Labour with a majority of only 428 votes over the Conservative candidate.[5]

In the 2017 general election, Lynch increased her majority to 5,376 (11.1% of those voting) over the Conservative candidate, Chris Pearson.[6]

Lynch made her maiden speech in the House of Commons on 9 June 2015.[8] She stated her priorities as being Human Rights, the UK's relations with Europe and the protection of services at Calderdale Royal Hospital.[9]

Lynch was a member of the Environmental Audit Committee from July to October 2015 and was appointed to the Procedure Committee in February 2016.[10] Lynch was appointed as an Opposition Whip in the Commons on 18 September 2015.

Lynch is the chair of the All-Party Parliamentary Group on Fairtrade[11] and a Co-Chair of the British Museum group and Population, Development and Reproductive Health group.[9]

Lynch has also been a member of All-Party Parliamentary Groups on Migration, Britain-Palestine, Labour Friends of Palestine and the Middle East, Art and Health, Kashmir, Policing and Rugby Union.[9]

She was reappointed to the front bench by Labour leader Jeremy Corbyn on 3 July 2017, taking on the role of Shadow Flooding & Coastal Communities Minister within the Environment, Food and Rural Affairs team.[13][14]